The present invention relates to a recording system capable of multi-color recording of data and, more particularly, to a developing apparatus for a recording system, capable of multi-color recording of an electrostatic latent image.
A developing apparatus of a conventional recording system which can record data in two colors, e.g., black and one chromatic color comprises drum-like photoconductive member 1 as a recording medium on which an electrostatic latent image is formed, as shown in FIG. 1. First charger 3, first exposure unit 4, first developing unit 5, second charger 6, second exposure unit 7, and second developing unit 8 are arranged along rotating direction 2 of photoconductive member 1. Pre-transfer charger 9, transfer charger 10, separation charger 11, cleaner 12, and eraser lamp 13 are sequentially arranged on the downstream side of second developing unit 8. In this developing apparatus, after photoconductive member 1 is uniformly charged by first charger 3, a first electrostatic latent image is formed on photoconductive member 1 by first exposure unit 4, and the latent image is visualized in a first color by first developing unit 5. Then, after photoconductive member 1 is uniformly charged by second charger 6, a second electrostatic latent image is formed by second exposure unit 7, and the latent image is visualized in a second color by second developing unit 8. As the first developed toner is charged by second charger and the second developed toner isn't charged, there is a different of transfer condition between two toners. So photoconductive member is charged by pre-transfer charger 9. After precharging, two color images is transferred onto paper sheet 14 by transfer charger 10. Then, paper sheet 14 is peeled from photoconductive member 1 by separation charger 11, and is then guided toward a fixer (not shown). After the transfer operation, residual toner remaining on photoconductive member 1 is cleaned by cleaner 12. Finally, the latent image on photoconductive member 1 is erased by eraser lamp 13. In this manner, one cycle is ended.
In general, first developing unit 5 is used for black-color printing most frequently in a multicolor printing mode, and second developing unit 8 is used for printing in another chromatic color. In each of developing units 5 and 8, a developing roller as a developing agent carrier opposes photoconductive member 1 in a non-contact manner. The developing roller is rotated at the same peripheral velocity as that of photoconductive member 1, and the latent image on photoconductive member 1 is developed by toner fed from the developing roller.
However, in two-color developing processes described above, a developing state of first developer 5 located at the upstream side along the moving direction of photoconductive member 1 is insufficient, that is, the density of a line image is sufficient but the image density of a solid portion is insufficient. Thus, multi-color printing with high quality cannot be performed.